Aluminum is the metal most prominently used in aircraft assembly. Structural joints of aircraft are adhesively bound together. However, many adhesives do not adhere well to the aluminum substrate. To improve the adhesive strength in the joint areas, it is known to apply an electrodeposition coating to the aluminum substrate. A preferred coating in this regard is derived from a phosphated epoxy resin that is prepared by reacting an epoxy resin such as polyglycidyl ether of a polyphenol with phosphoric acid. The coating is applied by anionic electrodeposition and adheres very well to aluminum substrates and to subsequently applied adhesives. One problem with the electrodeposition coating is the formation of pinholes in the coating which give a rough coating with poor appearance. Also, the pinholes can be a point of failure in the coating.